The invention relates to an apparatus for sheeting deep trenches, and includes pairs of vertical support rails arranged along a trench. The support rails of each pair of support rails being arranged at the same distance opposite each other. A rigid strut frame holds support rails of a pair of rails at a distance from each other and is form-lockingly displaceable on the support rails. The apparatus also has large-surface outer sheeting plates and inner sheeting plates the vertical edges of which are vertically displaceable in guide channels of the support rails. The support rails have two side walls spaced from each other which, together with an outer wall and an inner wall, form an at least partially closed box beam, and the guide channels are formed, at least partially, by outer sides of the side walls, guide flanges, which lay in the plane of the outer wall, and support flanges which are spaced from guide flanges.
Such an apparatus is disclosed in German publication DE 40 28 832 A1. In the known apparatus, the inner wall of the support rail adjacent to the trench, which is formed as a box beam, is arranged on the longitudinal edge of the support rail adjacent to the trench. This inner wall extends up to the outer ends of support flanges which are bent out of the side wall. At the side edges, this inner wall has a bent-out C-shaped portion which forms a relatively wide guide rail for vertical rails secured to the strut frame. The relatively large width of the guide rails for the strut frame makes it more difficult to insert the strut frame in the guide rails formed by the C-shaped portions. Furthermore, because the inner wall extends up to the outer ends of the support flanges, it is unnecessarily heavy.